Commercial vehicles typically transport loads that can vary substantially in amount between different loads. When maintained at a relatively constant air pressure, the tire on such a vehicle will undergo changes to the shape of the contact patch as the loading is varied. As a result, the wear life of the tire's tread will be adversely affected.
Systems have been developed that allow for the addition of air to a tire in order to maintain a preset pressure. For example, commercial vehicles such as heavy duty truck and trailer combinations may be equipped with an air source and pressurized air storage systems for adding air to one or more tires if the measured air pressure falls below a predetermined value. In addition, systems have been provided for determining the load on a given axle based upon, e.g., the air spring operating pressure. However, none of these systems provide for automatically increasing and decreasing tire air pressure depending upon changes in the loading of the tire as the vehicle is used, much less provide for adjusting the pressure of the tires to a specific pressure based on loading in order to optimize the life of the tread.
In addition to variations in loads, the construction and positioning of tires used on commercial vehicles can also vary substantially. Commercial tires come in a variety of constructions and can include e.g., ribbed and non-ribbed tread. For a tractor and trailer combination, tire positions can include steer, drive, tag, and trailer positions. The impact on tread wear due to variations in loads will likely not be uniform between tires of different construction or between tires at different positions on a commercial vehicle. As a result, with load variations, the changes in air pressure required to minimize changes in the contact patch and improve tread wear will likely vary between the different tires and/or positions on the vehicle.
Manually adjusting tire air pressure based on changes in loading is not practical for a variety of reasons. Commercial vehicles may include a large number of tires; a well known example in North America includes the eighteen tires of the frequently used heavy duty tractor and trailer combinations. Manually inflating or deflating the trailer and/or drive tires each time a loading of the vehicle occurs would be time consuming and impractical.
A practice commonly followed by commercial vehicle operators is to employ a single, predetermined air pressure for all loads regardless of the variations between the loads. For example, a fleet operator may attempt to maintain all trailer tires above a certain minimum pressure setting but within the maximum pressure limit for a particular tire. The minimum pressure setting can be selected based on the minimum pressure recommended by e.g., guidelines provided by the Tire and Rim Association for the maximum load expected to be applied to the tire. Unfortunately, as previously stated, this constant approach is deleterious to tread life as changes in the load will cause variations in the contact patch. In addition, aside from the above described problems of a constant pressure approach, the pressure recommendations provided by the Tire and Rim Association are not based upon the optimization of tread wear for a given tire loading and do not suggest how such pressures might be determined.
Accordingly, a system for automatically adjusting the air pressure of a tire based on changes in loading is needed. More particularly, a system that improves tread wear performance by automatically adjusting the air pressure to a preferred air pressure as variations in loading of the tire occur would be very useful.